OP...it looks to me like you're over thinking this a tad bit as your question was already answered in a manner that is easily understood.
It isn't unheard of for a provider to post an ad...be it on here or P411...and not leave a posted rate, BUT...they will leave a note that says something in regards to contacting her either by PM or e-mail. In which case, you make contact and go from there.
Now if you come across an ad where no rate is posted and there are no other instructions...then...
1. Contact her and ask. Make sure you mention it's for her "time."
2. Consider the stupidity involved and just move along.
If you indeed do decide to make contact and she gets pissy with you...you either fucked up and didn't use proper etiquette or she's bat shit crazy and you could very well be labeled a "caveman" for just trying to figure out what the hell she's trying to do.
In a nutshell...unless its someone you REALLY want to see, just find someone else that knows how to conduct business in a somewhat professional manner.